The Player’s Guide to Compressor Pedals
Everybody loves distortion, delay, ands wahs. They are the big, dramatic effects that steal the show and make the sound of the guitar so distinct. But hidden underneath all the harmonics and echos, compression has had just as significant an effect on the guitar tone of many popular guitar styles. In a variety of styles including funk, country and blues, it has been used to add sustain or punch to a guitar part. It is so indispensable to some guitar sounds that you simply cannot sound like an authentic player without it.
Compressors work by controlling the dynamic range of the audio signal. A threshold amplitude (volume level) is set and any signal which exceeds that threshold is attenuated by a user-specified ratio. If the ratio is set at 2:1, for every two decibels the amplitude exceeds the threshold, the compressor attenuates (diminishes) the signal to one decibel above the threshold. Similarly, a ratio of 3:1 means that for every three decibels the amplitude exceeds the threshold, the compressor attenuates the signal to one decibel above the threshold. This has a lot of uses. It reduces the highest amplitude portion of the attack (when the pick hits the strings) so that the signal is smoother. This creates sustain, as the signal will remain at the same volume for longer. A compressor can also be used to cut the highest volumes while boosting the lower volumes using the output control, evening out the dynamic range of the whole signal and ensuring the lower dynamics are audible.
The addition of sustain is particularly of interest to blues and rock players as a held note can be kept at the same volume for an extended period of time. Country players love to use compressors to balance out the volume of their hybrid picking “(or chicken-pickin’”) techniques, an approach which utilizes both pick and fingers and can result in uneven attacks. Funk players use compressors to balance the volume and punch of muted rhythm parts. Rock and blues players use compression to add sustain to their leads.
Common Compressor Controls
Threshold- Sets the decibel level at which the signal will be compressed.
Ratio- Sets the ratio of amplitude reduction once the volume passes the threshold.
Sustain- This potentiometer merges the threshold and ratio into one setting as an overall compression effect.
Attack- Controls the amount of time before a signal exceeding the threshold begins compression. A very short attack time will result in a signal immediately being compressed while a longer attack time will create a more gradual compression until the signal reaches the desired ratio.
Release- Sets the amount of time after a signal drops below the threshold before compression is removed. A short release time means compression is removed instantly after dropping below the threshold while a longer release time results in its being removed more gradually.
Level- Controls the output volume of the compressor pedal. This allows players to use the compressor to smooth out peaks in the signal while compensating for any reduction in overall volume or boosting the overall signal.
Common Compressor Pedals
MXR Dyna-Comp- Simple, inexpensive, yet effective, this is a common stable on many players pedal boards. With just output and sensitivity knobs, you can get dial in the compression you need without a lot of hassle. A great choice for a first compressor pedal.
Boss CS-3- The “blue-box” is ubiquitous among top players yet quite affordable. The attack, tone, level and sustain knobs allow for more compression shaping than many pedals at the same price range.
Keeley Compressor- The gold standard of compression pedals. This pedal comes in two and four knob varieties and is the Mercedes-Benz of compressor pedals.
Common Compressor Settings
These settings are taken from the MXR Dyna-Comp manual. A digital model is available in Amplitube 4, which I use to teach my students about effects pedals.
Nashville- By raising the output and applying light compression, this setting will even out the discrepancies in amplitude between notes attacked with a pick and those attacked with fingers, a characteristic of the hybrid-picking style of country players. This is great setting if you are looking for a Brent Mason or Brad Paisley style tone.
New Wave Squash- To get a great funk rhythm tone, we need to even out the dynamics between a muted strum and an attacked chord. A high output and moderate compression lets us get the rhythm tone of a James Brown or Parliament tune.
Nasty Bottleneck- When the output and compression are maxed out, the signal will come out at a very similar volume no matter how you attack the strings. This setting can be used as a boosting effect for leads.
Signal Chain Placement
As compression works on the volume of a signal, it is classified as a gain-based effect. Therefore it is best placed at the beginning of a signal chain before any distortion or overdrive pedals.